Microphone



8, 1959 A. R. CAMMACK 2,900,453

MICROPHONE Filed April 16, 1957 HHllii' lulllli.

IN VEN TOR.

United States Patent MICROPHONE Arthur R. Cammack, Houston, Tex.,assignor to Associated Engineering & Equipment Company, Inc., Houston,Tex., a corporation of Texas Application April 16, 1957, Serial No.653,233 3 Claims. or. 179-4155 This invention pertains toelectroacoustic transducers, and more particularly to a microphoneadapted for use with a device for monitoring sound signals from afoghor'n placed on navigational hazard such as an offshore oil Well.

-It is an object of the invention to provide a microphone that will beselectively responsive to foghorn sounds.

It is a further object of the invention to provide a microphone thatwill be waterproofl corrosion resistant, and rugged enough to withstandexposure to the elements and rough handling such as are to be expectedin the intended'monitoring service.

Another object of the invention is to provide such a microphone thatwill be of moderate size.

Still another object of the invention is to provide such a microphonethat will be highly sensitive to the expected foghorn signals.

A further object of the invention is to provide such a microphone thatis inexpensive to manufacture.

Other objects and advantages of the invention will become apparent fromthe following description of a preferred embodiment of the invention,reference being made to the accompanying drawing wherein:

Figure 1 is a plan view of a microphone embodying the invention;

Figure 2 is a section taken on line 22 of Figure l; and

Figure 3 is an enlarged view of a portion of the apparatus shown inFigure 2.

Referring to Figures 1 and 2, the microphone comprises a cup shapedbrass housing having a hollow cylindrical side wall and a flat bottom11. An annular internal supporting flange 12 is disposed near the top ofthe housing below the upper edge thereof. A tension ring 13 disposed ontop of flange 12 carries an upstanding annular rib 14 integraltherewith. A sheet brass diaphragm 15 is stretched across rib 14. Anannular neoprene gasket 16 is disposed above the outer periphery of thediaphragm. Compression ring 17 is disposed on top of gasket 16. Aplurality of screws 18 extend through holes in ring 17, gasket 16,diaphragm 15 and ring 13 into threaded holes 19 in flange 12. Tighteningscrews 18 draws diaphragm 15 tighter over rib 14 of tension ring 13 andincreases the tightness of the diaphragm whereby the diaphragm may betuned to different fundamental frequencies. Gasket 16 makes a waterproofseal between the diaphragm and housing providing a waterproof chamberinside where the other elements of the microphone are mounted.

Diaphragm 15 is made of fairly thick material, e.g. 0.006 inch, so thatit can be resonate at a low frequency, e.g. 150 cycles per second andstill be of a fairly smaller diameter, e.g. about seven inches. Thethick diaphragm also provides a rugged wall closing the upper end of thehousing to protect the other parts of the microphone inside the housing.

A sheet metal frame has a conical side wall 30 and an Patented Aug. 18,1959 outturned peripheral flange 31, the flange 31 being secured to theunderside of ring 13 by screws 32. Between flange 31 and ring 13 is helda cardboard ring 33. A paper cone 34 is glued to the underside of ring33. At the small end of conical side wall 31 of the frame is an inturnedflange 35. A flexible disc 36 of impregnated cloth or paper or the likeis held at its periphery between flange 35 and a metal ring 37, therebeing screws 38 to clamp ring 37 to flange 35. Disc 36 forms a spider orsupport for electric coil 39 which is glued or otherwise securedconcentrically to disc 36. Disc 36 is also glued to the disc shapedportion 40 at the small end of cone 34. Cone 34 and spider disc 36combine to form an exceptionally rugged and stable supporting means forcoil 39. Both this cone and spider are corrugated as shown at '41, 42 toincrease fiexibility in the direction of the cone axis withoutsacrificing radial stability of the coil support.

Coil 39 is coupled to diaphragm 15 by means of a beryllium copper wire50 which may have a diameterof .020 inch. One end of the wire protrudesthrough a hole in the diaphragm and is soldered thereto at 51 forming awatertight connection. As best shown in Figure 3, the other end of wire50 has a portion 52 extending at right angles thereto which is held in arecess 53 in a fibre disc 54 cemented to spider disc 36. An aperturedmetal disc 54 through which wire 50 extends is cemented to the top disc54 to retain end portion 52 of the wire in recess 53. Also, wire 50 issoldered to metal disc 54a at 55. The foregoing coupling means insures asubstantially effective coupling between diaphragm 15 and coil 39 so faras the fundamental vibrations of diaphragm 15 are concerned, in whichthe center of the diaphragm moves in the direction of the axis of thewire. At the same time the wire is ineflicient in transmitting diaphragmvibrations of other frequencies in which the center of the diaphragmoscillates about axes in the plane of the diaphragm. The double supportfor the coil including the cone and spider further desensitizes thesystem to such harmonic modes of vibration of the diaphragm. Threefactors thus combine to render the microphone selectively responsive tothe expected foghorn signal:

(a) Tuned diaphragm (b) Wire coupling (0) Dual coil support Likewise,the strong brass diaphragm, wire, and dual coil support provide anexceptionally rugged construction.

Beyond flange 35 frame 30 extends axially a short distance at 60 andthen inward radially at flange 61 which ends in an aperture 62 closelysurrounding coil 39. A V-shaped yoke 63 of magnetic material having inone arm thereof an aperture 64 concentric with aperture 62 is spotwelded to flange 61. A cup 65 of magnetic material is secured to otherarm of the yoke. Disposed with cup 65 is a cylindrical permanent barmagnet 66 extending inside coil 31 flush with the apertured arm of theyoke. The permanent magnet cup, and yoke and the annular air gap betweenthe end of the permanent magnet and the aperture in the yoke form amagnetic circuit. There is just suflicient clearance between the coiland the permanent magnet core inside it and the apertured portion of theyoke outside it to allow the coil to move freely in the magnetic field,the air gap to generate electric currents in response to movements ofthe diaphragm in the direction of the coil axis.

The ends 70, 71 of the coil are connected in the spider disc 36 to theends of flexible wires 72, 73, which in turn are connected in cone 34 toflexible wires 74, 75, which are connected in the frame 30 to wires 76,77 leading to impedance matching audio frequency transformer 78 mountedon the yoke 63. An insulated cable 79 extends from transformer 78through a rubber grommet 80 or other watertight sealing means aroundaperture 81 in the bottom 11 of the cup shaped housing of themicrophone.

The air chamber formed by the cup shaped housing serves the dual purposeof providing protection for the principal parts of the transduceragainst the weather and mechanical blows and at the same time providingsufiicient air volume to prevent substantial damping of the diaphragm,this latter factor being especially important where the diaphragm isexpected to respond strongly to sounds of low frequency.

The overall construction of the apparatus is particularly well adaptedto inexpensive manufacture and easy maintenance. The wire 50 extendsthrough the diaphragm 15 to the exterior of the microphone and issoldered thereto on the outside so that in assembling or disassemblingthe microphone it is only necessary to free this soldered connection toenable the diaphragm to be assembled with or disassembled from theremainder of the microphone. On the other hand, the diaphragm andtransducer can be handled as a unit if desired since by unscrewingscrews 18 the entire internal assembly can be lifted along with ring 13.

While a preferred embodiment of the invention has been shown anddescribed many modifications thereof can be made by one skilled in theart without departing from the spirit of the invention, and it isdesired to protect by Letters Patent all forms of the invention fallingwithin the scope of the following claims.

I claim:

1. An electroacoustic transducer comprising a cup shaped housing, anannular rib, means supporting said rib at the mouth of the housing, adiaphragm supported by said rib and having its outer periphery extendingradially beyond said rib, means securing the periphery of said diaphragmto said housing, the last said means being adjustable to tune saiddiaphragm to a desired frequency, means mounted in said housing andincluding relatively movable portions for generating electricity inresponse to motion of one of said portions relative to the other of saidportions, and a wire connecting one of said portions of the last saidmeans to the center of said diaphragm.

2. An electroacoustic transducer comprising a cup shaped housing, anannular rib, means supporting said rib at the mouth of the housing, adiaphragm supported by said rib and having its outer periphery extendingradially beyond said rib, means securing the periphery of said diaphragmto said housing, the last said means being adjustable to tune saiddiaphragm to a desired frequency, magnetic circuit means in said housinghaving an annular air gap and producing a magnetic field across saidannular air gap, an electric coil, means supporting said coilconcentrically in said air gap for oscillatory axial movement thereinwhile restraining said coil against transverse motion therein, saidsupporting means comprising a first flexible peripherally supported discand a second smaller disc concentric therewith connected at itsperiphery with a flexible cone, said cone being supported at its endopposite said disc, said discs being centrally connected to each otherand supporting one end of said coil, and a wire connecting saidsupporting means to said diaphragm.

3. An electroacoustic transducer comprising a hollow cylindrical housingof rust resisting metal, a closure for one end of said housing, saidclosure being made of rust resisting metal, a flexible diaphragm of rustresisting metal closing the other end of said housing, a metal framedisposed inside of said housing and secured to said housing, said framehaving a central opening therethrough concentric with said housing, amagnetic yoke secured to said frame, said yoke having an aperturetherein concentric with said opening, a permanent bar magnet having oneend magnetically connected to said yoke and its other end disposed insaid aperture forming an annular air gap, a flexible disc secured tosaid frame over said opening, an electric coil carried by said discextending into said air gap for axial movement therein, and a wireconnecting said disc and the center of said diaphragm, said housing andend closure being watertight to provide a weather resisting ruggedprotective means surrounding the other above enumerated portions of thetransducer.

References Cited in the file of this patent UNITED STATES PATENTS1,862,552 Schlenker June 14, 1932 FOREIGN PATENTS 442,485 Italy Nov. 23,1948

